DOS (disk operating system, DOS) is a well-known operating system that is very flexible and easy to use for general users and program designers. DOS provides many good functions. FIG. 1 is the flow chart for the process to open a file in DOS environment for a prior art example. First, in the case of using C programming language, an instruction of opening the file which is named as "patent" is stared to execute in C programming language library. The proper API (application programming interface, API) function, which provides by DOS, will be subsequently invoked. The general format of the API function invoked is presented as following:
fopen(filename, mode) PA1 fopen("patent", "r")
In order to open the file which file name is "patent", the API function will be as following:
According to the parameters ("patent" in this case) passed to the API function, the API function will search the directory cluster in the disk driver for the file. When the file is found, open and read the content of the file. However, DOS is mainly designed based on English. There are many problem caused by using DOS in other language systems.
A character is presented by two bytes for most of the language systems in Asia, such as Traditional Chinese, Simplified Chinese, Japanese and Korean etc. These language systems are called as double-byte language systems. In the double-byte language systems, a character is composed by two ASCII codes. When these double-byte characters are processed, these double-byte characters need to be converted to two corresponding ASCII codes so that these double-byte language system which contains numerous characters can be processed by computer. The ASCII codes of the upper case and the lower case for the same English alphabet are different. Both the ASCII codes of the upper case and the lower case will be used to present a double-byte character in the double-byte language systems. However, DOS will treat the upper case and the lower case for the same English alphabet without difference. A error of identification will consequently occur when a file, which is named in double-byte language, is to be read in DOS, because DOS cannot identify two double-byte characters that one contains the upper case and the other contains the lower case for the same English alphabet.